The present application relates to an earthmoving system of the type that incorporates a bulldozer for contouring a tract of land to a desired finish shape and, more particularly to a bulldozer system in which the position of the cutting tool is continually updated by GPS receivers and the position is corrected using low latency, feed forward correction signals generated in response to outputs from gyroscopic sensors and an accelerometer that monitors vertical acceleration.
Various control arrangements have been developed to control earthmoving devices, such as bulldozers, so that a tract of land can be graded to a desired level or contour. A number of systems have been developed in which the position of the earthmoving apparatus is determined with GPS receivers. In such systems, a site plan is developed with the desired finish contour. From the tract survey and the site plan, a cut-fill map is produced, showing amounts of cut or fill needed in specific areas of the tract to produce the desired finish contour. The information is then stored in the computer control system on the bulldozer.
The earthmoving apparatus determines the position of the cutting tool of the bulldozer using the GPS receivers mounted on the bulldozer body or on masts attached to the blade of the bulldozer. A computer control system calculates the elevation error of the blade based on the cut-fill map and the detected planar position of the apparatus. The elevation error may be displayed for the operator of the bulldozer who can then make the appropriate adjustments manually. Alternatively, the computer may automatically adjust the elevation of the blade to reduce elevation error.
One limitation encountered with such systems is that the GPS position computations are made at a relatively slow rate, e.g. on the order of several times per second. As a consequence, the control system is only able to determine the position of the machine and the position of the cutting blade relatively slowly. This significantly limits the speed of operation of the bulldozer, especially over rough terrain. It will be appreciated that a bulldozer frame may pitch fore and aft, may pitch from side to side, and may yaw right and left as the bulldozer moves across a bumpy area of a job site. Additionally, the frame of the bulldozer may bounce up and down. All of these movements of the frame are transferred to the blade in front of the bulldozer and may even be amplified, since the blade is positioned well ahead of the center of gravity of the machine, the point about which the rocking and yawing occurs. Lowering the speed of operation of the bulldozer to permit the GPS control system to compensate effectively for the uneven surface conditions of the job site results in an undesirable reduction in productivity.
It is seen that there is a need, therefore, for an earthmoving system and method having a bulldozer or other machine, and including GPS receivers and a control in which compensation is made for inaccuracies in the cutting blade position that would otherwise result from pitching and vertical movement of the bulldozer frame.